Gas-retaining fabric



Patented Aug. 1 6,

PATENT OFFICE GAS-RETAININ G FABRIC Theron P. Sager and David F.Houston, Washington, D. C.

No Drawing. Application August 22, 1936.

Serial No. 97,448

2 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) This invention relates to the treatment of fabrics employedfor the retention of lifting gases in lighter-than-air craft, and itparticularly relates to the provision of a gas impermeable coating forsuch fabrics.

One object of the invention is to provide a coating material which maybe readily applied by calendering, brushing, spraying, or spreading.

Another object is to provide a coating which shall be highly flexibleand durable under varying conditions of atmospheric exposure.

It is customaryin the construction of gas-retainlng fabrics to apply afilm or coatingto the surface of-the fabric which will prevent the dif-'fusion of the enclosed'gases. Rubberized fabric has been employed as agas-retaining medium. Rubberized fabric is relatively. inexpensive andeasily manufactured,. but a film of rubber is inherently permeable togases and the use of 'rubberized fabric in the construction of gas cellsresults in a high loss of lifting gases. varnishes, lacquers, and dopeshaving cellulose derivatives as their basic" materials. have beensuggested as gas retaining films. Those which have been proposed havenot, however, been wholly satisfactory, either because of their highrate of diffusion to gases or because they tend to crack on flexing v ofthe coated fabric. Another class of materials which is employed ascoatings for gas-retaining fabrics includes substancesrsuch asgoldbeaters skin,. gelatin, and regenerated cellulose. These materials,while highly impermeable to lifting gases, all have a fault in common inthat they are maintained in a flexible condition by the pres- .:.5 enceof glycerol or'slmilar hygroscopic plasticizer.

The presence of a hygroscopic plasticizer causes a wide variation in theweight of thecoated fabric under varying conditions of atmospherichumidity. A further objection' to the use of these materials is thatthey are readily subject to attack by mold and bacteria.

This invention 'consists in the discovery that films containing anoleflne-polysulphlde reaction product are highly impermeable to hydrogenand 4 5 helium, and in addition the foregoing disadvantages-ofgas-retaining fabrics formerly proposed may be overcome by employing asa coating on such fabrics an oleilne-polysulphide reaction product. Afabric thus coated possesses the char- .30 acteristlc flexibility ofrubber but differs from rubber in having a low permeability to'llftinggases. The term oleflne-polysulphide reaction product relates, to aplastic material obtained by the interaction of alkaline or alkalineearth poly-.

- sulphides and organic compounds containing methylene or substitutedmethylene groups, and

particularly to additive halogen derivatives of such compounds. Such amaterial may be appliedto a fabric by any of the .customarily'employedmethods. In the form of a plastic mass it may be calendered. Dispersedina suitable solvent it may be sprayed, brushed, .or spread with aspreading machine. The material may be employed ,as an impermeablecoating unmixed with any-other material and not subjected to any heattreatment; To. obtain, however, the.

most satisfactory physical characteristics it has been found desirableto compound it with varying amounts of rubber, pigments, accelerators,and vulcanizing agents. Likewise, it has been found desirable to curethe coated fabric at ele;- vated temperatures to obtain the mostsatisfactory strength and flexibility. A fabric coated with anolefine-polysulphide reaction product is remarkably resistant to waterand organic sol- I ven'ts, notably the hydrocarbons. It has also beenfound to be highly impermeable to hydrogen and helium.

In the following examples illustrative of our invention theolefl'ne-polysulphide reaction product referred to therein was of agrade known as "Thiokol 13, prepared by the Thiokol' Corporation,Yardville, New Jersey. The scope of this inventionlis not, however,limited to this particular grade of material.

Example 1 One hundred gramsof olefine-polysulphide reaction product wasdissolved in 1000' grams of carbon disulphide and applied to a closelywoven balloon fabric by brushing. The balloon fabric weighed 2 ouncesper square yard. The coating was dried at 125 F. until all residualsolvent was driven off. The coated fabric weighed 5.7 ounces persquare'yard and gave a diffusion rate of 0.5 liter, per square meter per24 hours.

Example 2 A material serving as another example was composed as followsinparts by weight:

Oleflne polysulphide reaction product--- Zinc oxide 10Tetramethylthiuram disulphide 0.2

then applied to a closely woven balloon fabric by brushing on aplurality of coats. The coated fabric was cured in a drum in open steamfor 60 minutes at 264 F.

The cured fabric, which weighed 5,6 ouncesper square yard, gave adiffusion rate of 0.4 liter per square meter per 24 hours.

Example 3 A mixture composed in parts by weight of the following wasprepared:

Olefine-polysulphide reaction product 100 Smoked sheet rubber 10 Zincoxide 10 Carbon black 20 Tetramethylthiuram disulphide 0.25

Example 4 This example illustrates the adaptation of our invention to avariation of coated fabric construction. To a closely woven balloonfabric was applied the following in parts by weight:

Smoked sheet rubber 100 Zinc oxide 10 Stearic acid 1 Sulphur 0.6Tetramethylthiuram disulphide 0.25 Mercaptobenzothiazole 1 Benzol 3600The solution was applied to the fabric with a spreading machine to theamount, upon evaporation of the solvent, of 0.6 ounce per square yard.

To the preponderan-tly rubberized surface of this fabric was thenapplied a material composed in parts by weight of the-following:

Oleflne-poly sulphide reaction product--- 100 Smoked sheet rubber"; 50Zinc oxide 10 Tetramethylthiuram disulphide 0.25 Beta trichlorethane1800 The solution was applied with a spreading ma.- chlne. The amount ofcoating applied was 0.8 ounce per square yard.

To this coated surface was then applied the following mixture in partsby weight:

Oieflne-polysulphlde reaction product 100 Zinc oxide 10Tetramethylthiuram disulphide 0.1

Beta trichlorethane 1100 The amount of coating deposited from this mix-The mixture was then dispersed ture was 2.6 ounces per square yard. Thecoated fabric was then heated in dry heat for 60 minutes at 264 F. Inthis method of construction the intermediate coating serves as anadhesive layer by which the outer coating of olefine-polysulphidereaction product is attached to the rubberized fabric.

In the foregoing examples the functions of the various compoundingingredients are as follows:

Rubber is added to improve the tensile strength of the compoundedmaterial. Zinc oxide is an important ingredient which materially assistsin altering the properties of the olefine-polysulphide reaction productduring the final heat treatment with the result that the material isrendered more resilient and resistant to abrasive action. Carbon blackincreases the toughness of the mixture. Tetramethylthiuram disulphide,mercaptobenzothiazole, sulphur and stearic acid improve the propertiesof the compounded material by assisting the curing of the rubber andtheolefine-polysulphide reaction product.

The foregoing examples are given merely for purposes of illustration.Numerous modifications are possible and will be apparent.

Other modifications and changes in the proportions and arrangements ofthe parts may be made by those skilled in the art without departing fromthe nature and scope of the invention, as defined in the appendedclaims.

' The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

Having thus set forth and disclosed the nature of this invention, whatwe claim is:

1. The method of providing a balloon fabric impermeable to lifting gaseswhich comprises applying a gas impervious continuous film to a closelywoven balloon fabric weighing approximately two ounces per square yard,the fabric being first rubberized before the continuous film is applied,the continuous film including a coating composition comprising anolefine-polysulphide reaction product and rubber, the oleflne-poly-,

sulphide reaction product being the basic ingredient of the compositionand providing the impermeability factor to the fabric, whereby thecompleted impermeable balloon fabric has its weight increased from twoand four-fifths to three times its original weight.

2. A balloon fabric impermeable to lifting gases comprising a closelywoven fabric weighing approximately two ounces per square yard, arubberized coating on said fabric and a continuous gas impervious filmon said rubberized fabric, said film comprising an oleiine-polysulphidereaction product and rubber, the oleflne-polysulphide product being thebasic ingredient of the composition and providing the impermeabilityfactor to the completed fabric, the completed fabric weighing from twoand four-fifths to three times the weight ofthe original fabric. I

THERON P. SAGER. DAVID F. HOUSTON.

